The present invention relates in general to equipment for mixing a vaporizable liquid with a gas flow, and in particular to a new and useful apparatus and method for admixing liquid anesthetics with respiratory gas supplied to a patient.
In medical equipment, in which any failure may lead to life-threatening conditions for the patient, it goes without saying that components or their arrangements are monitored by other components that function independently or that linkages exist in the equipment, which give signals if there are differences between the actual and nominal values. With the signal, visual or auditory alarms are set off and/or automatic corrective measures, such as the switching to reserve assemblies, are initiated. The following known apparatus does not have such control capabilities.
In this known apparatus for admixing liquid anesthetics into the respiratory gas to be supplied to the patient, a gas metering device is arranged in the respiratory gas feed to the patient and one or more injection pumps for the anesthetics are connected. It further comprises one or more cylinders with plungers that are adjustable in their immersion depth, in which the anesthetic supply ends. The immersion depth is dependent on the quantity of respiratory gas flowing to the patient in a manner which is controlled via levers. The anesthetic displaced from the cylinders by the immersion of the plungers is introduced or injected into the respiratory gas stream. The lever control can be effected by a double piston moving in a cylinder, the piston being moved alternately by the respiratory gas flowing in from the patient. This known apparatus is operated by the pressure of the respiratory gas. Besides the crucial disadvantage pointed out above, of lacking control, it must be noted also that the friction forces possibly varying at the gas double pistons and in the lever system must be overcome. Owing to this, then, the gas quantity per stroke and hence the anesthetic concentration changes, so that the concentration is thus friction dependent. The dry cylinder seals used are subject to heavy wear as well. (See German Pat. No. 12 71 902).